What’s Up With the Title?
None of Shakespeare's sonnets have titles, so we refer to them by number, in this case, 130. These numbers come from the order in which the poems were first published in 1609. The order actually matters a lot, since the sonnets can be roughly separated into groups based on their subject matter. Sonnet 130 comes from a whole group of sonnets that scholars think are addressed to a "Dark Lady." They call her that because she has black hair and dark features, like we see in this poem.
You might also see this poem referred to by its first line, "My mistress' eyes are nothing like the sun." This puts a double emphasis on the first line, and has helped to make it a famously quotable line in English literature.